Title of Invention	A COMPACT AND LIGHRWEIGHT LEAD-ACID BATTERY
Abstract	A novel 16 Ah lead-acid battery for miners lamps and other applications is described and comprises extra-thin plates in a 2+3 arrangement in the cells, said arrangement being accomodated in substantiaJly the same batten' box width as of the pnor art 12 Ah battery. The thicknesses of the positive plates, negative plates and separator are 9 5(including gauntlet). 3.25 and I 3 mm respectively and plate height and width are lesser than in said 12 Ah battery. The positive plates comprise wider bottom caps(5 mm) and shorter spines(90 mm), the latter improving the castability thereof. The batten,' offers reduced active material packing density, current density and internal resistance and consequently reduced maintenance. The batten requires less electrolyte, a greater proportion of which is free electrolyte.

Title of Invention

A COMPACT AND LIGHRWEIGHT LEAD-ACID BATTERY

Abstract

A novel 16 Ah lead-acid battery for miners lamps and other applications is described and comprises extra-thin plates in a 2+3 arrangement in the cells, said arrangement being accomodated in substantiaJly the same batten' box width as of the pnor art 12 Ah battery. The thicknesses of the positive plates, negative plates and separator are 9 5(including gauntlet). 3.25 and I 3 mm respectively and plate height and width are lesser than in said 12 Ah battery. The positive plates comprise wider bottom caps(5 mm) and shorter spines(90 mm), the latter improving the castability thereof. The batten,' offers reduced active material packing density, current density and internal resistance and consequently reduced maintenance. The batten requires less electrolyte, a greater proportion of which is free electrolyte.

Full Text	This invention relates to lead acid batteries and more particularly to compact and light-weight load-acid batteries for such applications as miners cap lamps. Miners cap lamps are also referred to as miners lamps, miners safety lamps and by other terms. In this specification, the term miners lamo is used and is intended to cover the equivalent terms mentioned hereinabove and also said other terms used in the art. Miners cap lamps generally comprise lead-acid batteries that form the subject of this invention. In this specification, therefore, the terra batter,' (ies) refers to lead acid batteries unless otherwise required by the context. The battery of the invention is particularly relevant to miners lamps the batteries whereof are required to be compact and lightweight. In this specification, thcrelorc, Ihe application of batteries of the invention to miners lamp alone is considered. This is in the interests of conciseness and without affecting the scope of the invention. In this connection, it is stressed that there are other applications in which the compact, lightweight batteries of the invention could be used/adapted to. Lead acid batteries may be made/traded with or without the electrolyte thereof. If with the electrolyte, the electrolyte may be contained in the battery itself or in a container separate of the battery. The term 'lrad acid battery' in the description and claims of this specification is intended to cover within the scope thereof the abovementioned and other possibilities An electrical cell such as a lead acid cell provides electrical energy and comprisss a pair of conducting plates immersed in an electrolyte. A battery comprises a plurality of such cells interconnected, or interconnectible, in series, or in parallel or in a series-parallel arrangement. A cell comprises also a container that houses the cell plates and holds the electrolyte thereof. Two containers are involved in a battery, the cell container mentioned hereinabove and the battery container. As mentioned, the former houses the parts and contents of a cell while the latter houses the cells comprising the battery. In this specification, the former is referred to as the 'cell case' and the latter as the 'battery box' or 'cell box', both latter terms being interchangeably used in the specification. Battery boxes (cell boxes) comprise compartments for housing the cells thereof. In one construction, cells complete with their cell cases are housed in said compartments. In another construction, said compartments are adapted to function as said cell cases, that is, they themselves form said cell containers wherein said cell plates and electrolyte are housed. It will be noted that in this construction said cell cases (cell containers) become redundant which results in considerable reduction in the overall weight and volume of a battery. Said elimination (of cell cases) has the effect of improving the energy density of the battery, said energy density being the Ampere-hours (Ah) capacity per unit weight or volume thereof. Modem miners lamp batteries (miners batteries) are generally of said another construction wherein the cell boxes thereof are made of plastics. There are two reasons for the adoption of plastics therefor, one being that plastics offer considerable weight/volume savings in comparison to hard rubber cell boxes. The other is that transparent plastics cell boxes permit easy visual inspection of the contents of a cell. In the specification further hereinbelow, therefore, as in the art, said compartments are also referred to as cell cases. Miners batteries are generally of 4V rating and comprise two lead acid cells each of 2V nominal capacity connected in series. This arrangement is also required by the standards adopted for miners batteries in various parts of the world, for example, IS:2512:1978 and BS:4945:1989. Thus a miners battery typically comprises a plastics cell box having two compartments therein each accommodating a lead acid cell, said two cells not comprising said cell cases, that is, said compartments themselves functioning as said cell cases as discussed hereinabove. The further specification hereinbelow is in reference to this construction only. This has been done in the interests of conciseness and without limitation to the scope of the invention. In principle, a cell comprises a pair of plates, one positive and one negative. However, in modern miners batteries, an additional negative plate is provided which is disposed such that the two negatives are located one on each side of the positive. This arrangement offers better utilisation of cell space in that both surfaces of the positive plate are then equally active in the cell process. This leads to a reduction in overall cell weight/volume and an increase in the energy density of the battery. It will be observed that in this construction, there are two pairs of positive-negative surfaces and consequently two separate current paths in the cell. The cell, in effect, constitutes two cells in parallel, that is, rather like a battery. However, said three plate construction is uniformly referred to in the field as a cell and this is the terminology adopted in this specification further hereinbelow. Thus, in this specification, a cell is understood to comprise three or more said plates arranged in an array wherein positive plates alternate with negative ones and the outermost plates of the array are negative, said array being housed in a said cell case (compartment). This is the construction referred to in the further specification hereinbelow although the arrangement in which the outermost plates of the array are positive is also within the scope of the invention. While reference has been made to arrays of three or'more said plates it must be emphasised that arrays of only three plates per cell are found in the miners batteries of prior art. No instance was observed of a miners battery construction wherein the cells thereof comprised more than three said plates each. Furthermore, there is apparently no indication of said array expansion beyond three plates having been considered in prior art. There is apparently no comment in prior art whether such an expansion would be desirable or not, and if so, whether feasible or not. This invention provides for a five-plate array and the consideration and development by this invention of said expansion to a five plate array is novel. Said five plate array is in the form of a 2+3 arrangement, that is, two positive and three negative plates. This is further elaborated hereinbelow. A miners battery of prior art comprises a plastics cell box having two said compartments (cell cases) each of which holds a lead-acid cell. A said cell has an array of three said plates, with the positive and negative plates being arranged alternately in the array and the two outermost plates being negative. The positive plate is of the tubular type and comprises a plurality of antimonial lead spines attached to a header (strap). Said spines and header are enclosed in a fabric gauntlet and the active material of the plate is packed in the spaces between said spines and gauntlet. The function of said gauntlet is to hold said active material and ensure good electrical contact between the active material and the header and spines. The function of said spines and header is to provide strength and rigidity to the plate as a whple. Said fabric gauntlet is required to prevent short-circuiting between the plates tiirough the active material and still to be permeable to the cell electrolyte and the ions contained therein. Said negative plates are of the flat type. A flat type plate comprises a grid(lattice) of cast, injection moulded or other construction and is generally of antimonial lead. The active material of the negative plates is applied to said grids in the form of a paste and the paste is pressed onto said grids and into the interstices thereof. As in the case of the positive plates, the negative grid and the active material thereof are enclosed in a fabric bag (envelope). Said grid provides support for the active material and furthermore, strength and rigidity to the plate as a whole. The function of said envelope is to prevent shorting of the plates through said active material of the negative plates. Said envelope is required to be permeable to the cell electrolyte and ions contained therein with the exception of antimony ions. Said negative envelopes are therefore, of microporous construction so as to prevent migration of antimony ions from the positive to the negative plates. Actually, the active material of negative plates is spongy lead while said paste comprises lead oxide. During the process of plate formation said oxide gets converted to spongy lead. However, the material on the plates is uniformly referred to herein as the active material whether the reference is to the plates before said formation or after. This has been done in the interests of conciseness and for simplifying the specification. The active material on the positive plate is lead peroxide and on the negative, spongy lead. Said active materials may further comprise one or more of several additives/components used in the art for improving the performance of the plates. The cell electrolyte comprises dilute sulphuric acid of the appropriate density range. Said gauntlets are generally of a polyester fabric and said envelopes of negative plates of polyethylene. Said polyethylene bags prevent shorting between plates, caused by oxide deposition at the cell bottom. Located between each pair of plates is a polyester separator whose function is to prevent electrical shorting between said pairs and also to absorb the cell electrolyte and render it immobile. A set of separators of a cell are designed to absorb about 85% of the electrolyte leaving only about 15% as free liquid. Said absorption helps in making the battery substantially spill proof. It also reduces gassing as the oxygen generated if any, at the positive plate, during charge or overcharge instead of rising to the top of the cell diffuses through said separator to the negative plate where it is reduced to water by reaction with the lead of the negative plate and the acid in the electrolyte. The battery is provided with a vent for evolved gases if any, the vent comprising a labyrinthine passage designed to prevent spillage of acid through the vent. The vent also performs the function of the topping-up opening by means of which the level of electrolyte in the cell can be topped up to the desired level. In the cells of miners batteries, said packs (assemblies) of plates and separators thereof are always under compression. That is, the total width of said packs is designed to be marginally greater than that of said compartments such that when the packs are placed in their compartments they are slightly compressed. Said battery box is provided with a lid that is joined to the former by means of processes such as heat-sealing, ultrasonic sealing, adhesive sealing, solution sealing or others as appropriate. Both said battery box and lid are usually of a transparent plastic such as a polycarbonate. Level markings are provided on said battery box to indicate the electrolyte levels in both fully charged and discharged conditions. Two terminal posts of high antimony lead alloy are provided one for the positive plates and one for the set of negative plates of a cell. They are joined to their respective plates by welding and protrude through said lid into the battery cover. Said posts form the cell/battery terminals at the top ends thereof. Said battery cover is generally of stainless steel and is fixed onto said lid. A said battery or cell may comprise more than one pair of said terminals. The battery is provided with a fuse located on said lid. The positive plates are usually of a high antimony lead alloy containing about four percent or more of antimony. For low maintenance batteries, a low antimony lead alloy is used for the positive plates, said low antimony alloy containing less than 3% antimony. Said low antimony alloys for plates often contain added grain refining elements, for example, selenium, copper, sulphur and others. The abovementioned alloys are also used for the negative plates. For negative plates of low maintenance batteries antimony-free calcium lead alloys are often used. However, use of said calcium-lead low maintenance alloys is generally confined to negative plates. The material of construction used for said cell boxes (battery boxes) are hard rubber, polycarbonates, ABS, polypropylene, fire retardant plastics and others. Described hereinabove is a most commonly used design of a miners battery in the art. It is stressed that numerous alternatives are available in the art substantially for all of the design aspects considered above and others, such as the material of the battery box and lid and the method of closure thereof; alloys used for said positive and negative plates; type and material of said gauntlets, envelopes and said separators; methods of joining the various components and others. In the interests of conciseness, said design alternatives (variants) are not elaborated in detail hereinbelow. However, it must be noted that the miners battery of the invention can incorporate and be adapted to, each said variant. Thus, each said variant is within the scope of the invention in so far as it is provided on, or adapted to the battery of the invention. A miners battery is expected to provide cyclic service, that is, working on a 24-hour cycle out of which during about 8 to 9 hours it is expected to be in the discharge mode. For the remainder of the time it is expected to be in the charge and storage mode. Typically, a miners lamp bulb draws about 0.8A which adds upto about 6.4 Ah of energy over a nine hour period. Considering a depth of discharge of about 75%, a 9 Ah capacity would be quite adequate for a miners battery and this is the standard capacity of one set of miners lamp batteries found in the art. Increasing the ampere-hour capacity of a miners battery would provide two options: i. increase the duration of said discharge mode while leaving the lamp (bulb) current unchanged; and . ii. increase in lamp current while leaving the duration of discharge unchanged. It will be noted that in the context of the application to miners lamps generally there is no scope of exercising the first option of increasing the duration of said discharge mode. The benefit of an increase of ampere-hour capacity can therefore, be realised only in the exercise of the second option, that is, increasing the bulb current. The art has therefore, developed 12 Ah capacity batteries for miners lamps wherein bulbs of higher rating, namely, 1,0A are used. Miners work-shifts are generally of about eight hours duration but where they are of twelve hours duration there is scope for utilising said first option of a longer discharge mode. This invention provides for a 16Ah miners battery and this is novel. The 16 Ah novel battery of the invention comprises said novel 2+3 plate arrangement, .that is, two positives and three negatives per cell. Thus, the battery of the invention provides the option of still further increase in bulb current so that bulbs of higher lumen rating may be used. Prior art has not considered/contemplated increase in ampere-hour rating beyond said 12 Ah perhaps because of the apparently insurmountable nature of difficulties observed by these inventors in carrying out said array expansion within the confines of the standard dimensions of prior art batteries and that laid down by various standards such as IS;2512:I978. This invention has provided said increased energy capacity together with said larger array, that is, said 2+3 arrangement within a battery box of substantially the same dimensions as of the said 12 Ah battery of prior art and as provided for by the abovenamed Indian standard. This is a further novel feature of the invention. Thus, the 16 Ah battery of the invention can be used in a miners cap lamp assembly comprising say a bulb drawing 1.25 A. Such a bulb would draw about 11.25 Ah over a nine hour period which would be around 75% of the battery capacity. Said cap lamp would then be 'operating in cycling service at a depth of discharge (DOD) of around 75% which is quite within the limit generally accepted in the art for lead acid batteries in cyclic service. . The battery of the invention also provides the option of using it in a cap lamp drawing a lesser current for example, with 1A bulbs as used in the 12 Ah miners batteries of prior art. In such an application, the battery of the invention would be operating at a still lower DOD value that would have the effect of enhancing the cycle life thereof. There would also be added advantages of reduced gas evolution and electrolyte loss (water loss) and reduced rate of irreversible sulphation of the plates. The object of the invention was to develop a compact, lightweight battery having a higher energy capacity of 16 AH as opposed to the 12 Ah capacity of prior art batteries. A further object of the invention was to provide this additional capacity by addition of a pair of plates, one positive and one negative to the 12 Ah miners battery of prior art. That was to change said array configuration of (1+2 one positive and 2 negatives) of said prior art battery to a (2+3) configuration comprising two positives and three negative plates. A still further object of the invention was to obtain said increased capacity and said (2+3) arrangement within the battery box of same width as provided for in the batteries of prior art. A still further object of the invention was to develop extra-thin plates such as to allow said 2+3 arrangement within the battery box of substantially the same width as in the batteries of prior art. A still further object of the invention was to minimise the thickness of the separators with a view to accommodate said 2+3 arrangement as also to increase the proportion of free electrolyte in the cells. A yet another object of the invention was to minimise the maintenance requirements of the battery. It will be observed that the increase in capacity from prior art to the battery of" the invention is about 33-1/3%. If this increase of capacity were to be provided by increasing the quantity of the active material on the plates both the packing density of the material on the plates and the current density of the plates would be correspondingly higher. The consequences of an increase in current density would be an increased tendency towards gassing. Further, the added active material would add to the internal resistance of the cell and this would enhance the voltage drop across the cell both during charging and discharging. This again will result in increased tendency towards gassing. Increased gassing requires increased maintenance attention to the battery in the form of more frequent toppings-up of the cells. Increasing said packing density has an adverse effect on the porosity of the active material mass on the plates, particularly in case of tubular positive plates. One effect of decrease of said porosity is a decrease in the discharge current. It also leads to a poorer DOD. This invention has achieved the object of minimising maintenance while avoiding the drawbacks mentioned hereinabove, by providing said increased capacity in the form of added plate surface. Thus, this invention provides for a (2+3) plate array configuration in place of the 1+2 array of prior art batteries. Change from a 1+2 arrangement to a 2+3 arrangement with plate dimensions remaining unchanged would substantially double the active plate area. As only about one-third increase of capacity is desired this invention provides the option of decreasing the plate dimensions somewhat. Accordingly, in this invention the plate height and breadth have been reduced from that in the 12 Ah prior art battery that, as explained hereinbelow, resulted in improvement in battery performance. The approximate dimensions of said 12 Ah prior art battery and the 16 Ah battery of the invention are displayed in Table 1. Table -1 12 Ah Prior art battery 16 Ah battery of the invention Plate height in mm. 118 100.8 Plate breadth in mm. 66.7 57 The quantity of electrolyte provided in the 16 Ah battery of the invention can be somewhat greater, equal to or less than that in the prior art 12 Ah battery within the scope of the invention. In the embodiment described further hereinbelow, the quantity of electrolyte in the battery of the invention is somewhat less than that in the prior art battery such as to maintain substantially the same level of electrolyte in both. It may be noted that the dimensions of the battery box of the invention are substantially same as that of the 12Ah prior art battery. The battery of the invention therefore meets the requirement of the non-spillability test under IS 2512:1978. This invention provides for extra-thin positive and negative plates and this is novel. The thickness of a positive plate in a 12 Ah battery of prior art is about 10.5 mm and of a negative plate about 3.60 mm. These thicknesses have been considered irreducible in prior art. This invention provides reduced plate thicknesses while at the same time adequate strength and rigidity for the plates. The novel thicknesses in the batteries of the invention are: for positive plates about 9.5mm and below and for negative plates about 3.4 mm and below. The positive plate thickness mentioned hereinabove includes the gauntlets thereof while for the negative plates the thickness figures exclude the envelopes thereof. Said extra-thin plates are novel and result in slimmer plate packs. This makes it possible to accommodate a 2+3 plate configuration in the same generally 42 mm wide battery box as that used by the prior art 12 Ah battery. It may be mentioned that 65 mm is the maximum value of the. width laid down by IS:2512:1978 for miners cap lamp batteries. Thus, the width of the battery box in the battery of the invention is considerably less than that laid down under IS 2512:1978. The cell internal resistance is also reduced by the use of slimmer plate packs that incorporate said extra-thin plates of the invention. The separators in the batteries of the invention are of the same material as that in the 12 Ah prior art battery but are of reduced thickness. This is novel. This has been done to bring down the width of said 2+3 plate pack sufficiently to be able to house it in the battery box of prior art. Said separator thicknesses are about 1.35 mm and 8.5 mm respectively for the battery of the invention and the prior art battery. This reduction of separator thickness also brings down the internal resistance of the cell. The separators comprise polyester pads. Reduction in separator thickness could be expected to lower the amount and availability of the acid electrolyte in contact with the plates. This effect is countered in the battery of the invention by the increased proportion of tree electrolyte available in the battery of the invention in contrast to batteries of prior art. Any adverse effects of the reduction in thickness of the plates from that in prior art have been countered by the following factors as a result of which the performance of the battery of the invention is equal to and in some respects superior to the prior art batteries. i. increased said porosity obtained because of reduction in quantity of active material per unit plate area; ii. the availability of a larger proportion of free electrolyte following the reduction in separator thickness; In summary the novel and advantageous features of the battery of the invention are: i. a higher electrical capacity and a higher energy efficiency of watt-hr/kg and watt- hr/cu.cm; , ii. a 2+3 array; Ui. reduced plate thicknesses leading to reduced internal resistance of ceil, iv. reduced separator thickness leadinp to reduced internal resistance of cell; v. less tendency towards gassing because of reduced internal resistance of cell, reduced packing density of active material on plates and reduced current density in the cdl; vi. greater proportion of free electrolyte than that in prior art battery; vii. use of a low maintenance alloy (low antimony lead alloy) for the positive plates; viii. increased height of the bottom caps for the positive plates which reduces the risk of shorting still further over that in prior art batteries; and ix. reduced height of said spines .which improves the castability thereof, in particular casting under pressure. According to the invention, therefore, there is provided a compact and light-weight lead-acid battery for such applications as minsrs lamps, comprising a plurality of lead acid cslls, each said cell comprising an array of alternating positive and negative plates with separators interposed therebetween, characterised in that at least one said array therein comprises five said plates. The battery of the invention comprises two or more lead acid cells wherein one mcc or all of said cells may comprise the novel 2+3 array, that is, pack of two positive and three negative plates together with their separators. In one embodiment which is particularly applicable to miners lamps, the battery of the invention comprises two said cells each of which comprises said novel 2+3 array of plates. The embodiment described further hereinbelow is of a miners battery and is in general accordance with IS 2512:1978 for miners batteries. This invention provides for extra-thin plates, that is, positive plates of thickness equal to. or less than about 9.5 mm and negative plates of thickness equal to or less than about 3.4 mm. One, more or all of the plates of the battery of the invention may comprise said extra-thin plates. Said thickness values include the gauntlets in the case of positive plates whereas in the case of negative plates the thickness refers to the bare plate exclusive of the envelope thereof. In the embodiment described, all the five plates of each of the two cells are extra-thin. The thickness of said plates in the embodiment described herein are about 9.5 mm and 3.25 mm respectively for the positive and negative plates. The invention also provides for slim separators of thickness 1.35 and below. The five extra-thin plates in a cell together with four of said slim separators constitutes a pack which is placed in a said compartment of a cell box. The width of said pack is such that when in position in said compartment it is under slight compression. The width of the pack in the compressed state comes to about 36 mm which together with the thickness of the sides of said compartment adds upto about 42 mm the outside width of the battery box. The Indian Standard IS:2512:1978 lays down a maximum width of 65 mm for the battery box of a miners battery. This figure includes the projections of the belt loops located on the surface of the battery box body. The embodiment described conforms to said standard in respect of the dimensional requirements and other requirements including the non-spillability test. The thickness of separators in the embodiment described herein is about 1.3 mm. The battery box including the lid thereof are of a transparent polycarbonate in the embodiment described and the sealing is by use of appropriate solvents. Other materials of construction for the battery box and lid such as polypropylene and the use of other sealing methods are within the scope of the invention. The positive and negative plates are both ofantimonial lead of about 2.5% Sb in the embodiment described. It is quite feasible to use other alloys such as are used in the batteries of prior art, such as, for example, calcium-lead alloys and these are within the scope of the invention. It is also feasible to use pure lead for plate construction but the use of both pure lead and said other alloys is associated with drawbacks. The option of using different alloys for the positive and negative plates is also within the scope ofthe invention. The positive plate comprises a header wherefrom extend said spines thereof. Each header has one or more connection lugs that are joined to a terminal post by welding or other means. Said terminal post extends through said battery box lid and into the space between said lid and the battery cover top. The top ofthe terminal post constitutes the battery terminal and is located in said space. The negative plate is in the form of a grid complete with the interstices thereof. Said grid plates are made by casting, injection-moulding, expansion or other processes. Various patterns and sizes of grids and interstices are used in the art and are within the scope of the invention. The active material is pressed onto the negative plate and into said interstices. The construction of said terminal posts, lugs and other components is similar to that in the case of the positive plates. A miners battery comprises two each of said positive and negative .battery terminals for each cell and the terminals of the two cells are connected in series to provide a nominal voltage of 4V for the battery. This is the construction provided in the embodiment described further hereinbelow. The gauntlets ofthe positive plates are of a polyester fabric in the embodiment but may be of one of several suitable fabrics provided in the art. The gauntlets are made from woven fabrics by stitching or heat-sealing. They are placed around said spines and the space between the gauntlets and spines is filled with the required amount of the active material of the positive plates. The lower end of the gauntlet, that is, of the positive plate is capped by a generally oval cup-like member. The function of said cap is to hold the active material and to prevent both shedding of the active material and shorting between plates. The gauntlets ensure adequate contact between the active material and the spines and prevent said shorting. The gauntlets are required to be permeable to the electrolyte and the ion components thereof. The envelopes of the negative plates are of woven polyethylene in the embodiment but several other materials are available for the purpose in the art and are within the scope of the invention. Said envelope is in the form of a bag made from polyethylene sheet /fabric and are formed by heat-sealing. Said bags are slipped over the negative plates, one for each plate. The bags prevent shorting of the plates and oxide deposition at the bottom of cells and are permeable to the electrolyte and the ions contained therein with the exception of antimony ions. Said separators consist of polyester pads in the embodiment described. They absorb the electrolyte in the pores thereof and render it substantially immobile. The absorption of the bulk of the electrolyte by said separators makes the battery substantially non-spi liable. The quantity of the electrolyte in a cell is adjusted so that a certain amount of the pores in said separators remain unfilled, that is, free of electrolyte. The unfilled pores provide channels for diffusion of gases between plates. In particular, oxygen evolved if any, at the positive plates during charging or overcharging diffuses across to the negative plates where it is reduced to water by reaction with the spongy lead of the negative plates and the acid in the electrolyte. In this manner, water lost from the electrolyte by gassing is substantially returned back to the electrolyte making the battery substantially maintenance-free. Several other materials for said separators are provided in the art and are within the scope of the invention. The invention provides for said plastic caps of a larger height of about 5 mm than those provided in prior art. This further reduces the risk of shorting occurring through the lower ends of the positive plates. This is novel. Said spines in the battery of the invention are of a smaller length than provided in prior art. The decrease in said length has been partly possible because of the decrease in the height of the positive plates of the battery of the invention over that in prior art. In the prior art miners batteries, the length of said spines is of the order of 110 mm against a plate height of 118 mm. The decrease in the plate height of the battery of the invention over that in prior art provided scope for a proportionate reduction of said length. This invention has gone further in reducing said spine length down to about 90 mm and below. This has resulted in better castability of the header-lug-spines assembly that is, in reduction in rejects. This has been achieved while maintaining the performance of the battery of the invention to the level of the prior art batteries. Said spine length in the embodiment described hereinbelow is about 90 mm. In order to provide a clearer understanding of the invention, an embodiment thereof will now be described without limitation to the scope of the invention and with reference to the accompanying drawings wherein: Fig. 1 shows an isometric view of the battery of the invention; Fig. 2 shows an exploded view of said pack of plates and separators of the battery of the invention, and Fig. 3 shows the maximum dimensions ofa miners battery as laid down in IS:2512:1978 with the corresponding dimensions of the battery of the embodiment shown in brackets. Reference numeral 1 in Fig. 1 denotes the battery box (cell box) having lid 2 which is attached thereto by solvent welding. Cell box 1 comprises two compartments 3,4 which house the two cells of the battery. Each cell comprises a pack (assembly's, of positive plates 6 and negative plates 7 and the separators 8 thereof. Each positive plate 6 comprises header 9, spines 10 and connection lug 11 all made of a low-antimony selenium lead alloy. Header 9 and spines 10 of a positive plate are enclosed by a gauntlet 12 made of a polyester fabric. Each positive plate is provided with a plastic cap 13 at the lower end thereof. Said caps 13 are applied after the gauntlets 12 are filled with the active material 14 of the positive plates. Gauntlets 12 together with caps 13 hold the active material 14 and ensure good electrical contact between spines 10 and the active material. They also prevent shedding at positive plates and shorting between plates. Negative plates 7 comprise cast grids 15 of a low antimony selenium lead alloy. Grids 15 have interstices 16 that hold the active material 17 of the negative plates. Plate active material is applied to grids 15 and interstices 16 in the form of a paste which is pressed upon the grids and into said interstices. Negative plates undergo a process of formation during which said paste material is converted into spongy lead, the active material of the negative plates. Each negative plate 7 is enclosed in an envelope 18 which covers both sides thereof. Envelope 18 is of microporous polyethylene and is in the form of a bag that is made from polyethylene sheets by heat-sealing or solution-sealing. Gauntlets 12 and envelopes 18 hold the active material of the respective plates and prevent shorting between the plates. They allow free diffusion of the electrolyte 19 and ions between the plates. Located between each positive-negative plate pair 6,7 is a separator 8 that comprises a porous polyester pad. Pads 8 absorb electrolyte 19 and allow diffusion of oxygen gas from positive to negative plates. Most of the oxygen liberated, if any, at the positive plates thus eets transoorted to the negative plates where it is converted to water and returned to the electrolyte. Separators 8 allow diffusion of the electrolyte between the plates. Said connecting lugs U of a cell are connected to the positive terminal post 21 which extends upwards through said lid 2. The top end of terminal post 21 forms the positive terminal 22 and is located in the space between said lid 2 and battery cover 30. The lugs 23 of the negative plates 7 are also connected together and to the negative terminal post 24. Terminal post 24 similarly extends above said lid 2 and has the negative terminal 25 at the top end thereof. Vent openings 26 vent any gas that is released in the cell and that is collected in the space above the electrolyte. While most of the oxygen evolved at the positive plates diffuses to the negative plates through said separators and is recycled as mentioned hereinabove a small quantity thereof may collect above the electrolyte and is vented out of the cell. Said vent openings 26 include a non-spill device 27 which comprises a labyrinthine passage that allows gas to escape but holds back the electrolyte. The two vent openings 26 of the battery are solution-jointed to the battery box. A pair of level indicating marks 28 are provided for each cell. Said marks indicate the desired electrolyte level in the cell both in the fully charged and discharged condition thereof. During maintenance water is added to the cell to make up for the water lost if any. Said topping-up is made to the appropriate mark. Addition of water to the cells is done through said vents 26 that also function as openings for topping-up. Gaskets 29 are provided at terminal posts 21,22 to provide seal between said posts and lids 2. The battery is provided with top cover 30 that is of stainless steel. Cover 30 comprises insulating pads of PVC located on the top inside surface thereof so as to prevent shorting between said posts. Battery fuse 31 is located on lid 2. The material charged into the gauntlets 12 of positive plates 6 comprises a mixture of lead oxides which during the formation process of the plates gets converted to lead peroxide, the active material 14 of the positive plates. Similarly, the paste applied to the negative plate grids at the time of manufacture comprises lead oxide which during said formation process gets converted to spongy lead. Said spongy lead constitutes the active material 17 of the negative plates. Said active materials may contain one or more of several additives provided in the art for enhancing the performance of the battery. During discharge, the active material of both the positive and negative plates gets converted to lead sulphate which gets regenerated back to the respective active materials during the charging operation. Cover 30 is provided with looping/locking means 32 for the cable that would run from the battery of the invention to the cap lamp when the two are assembled. Means 32 ensure that said cable is not pulled off during use of the battery and the cap lamp. Belt loops 33 are provided on battery box 1 for attaching the battery to the waist-belts used by miners. Various embodiments and variations other than described above which are within the art are within the scope and spirit of the invention. We claim: 1. A compact and light-weight lead acid battery for such applications as miners '^nps comprising a plurality of lead acid cells, each said cell comprising an array of alternating positive and negative plates with separators interposed therebetween, characterised in that at least one said array therein comprises five said plates. 2. The compact and light-weight lead acid battery as claimed in the preceding claim 1 wherein the outermost plates of the arrays are negative. 5. The compact and light-weight lead acid battery as claimed in the preceding claim 2 having a capacity of about 16 Ampere-hours. 4. The compact and light-weight lead acid battery as claimed in the preceding claim 3, wherein the thickness of said positive plates is equal to, or lower than, about 9.50 mm and of said negative plates is equal to, or lower than, about 3.4 mm. 5. The compact and light-weight lead acid battery as claimed in preceding claim 4, wherein the thickness of said separators is equal to, or lower than, about 1,35 mm. 6. The compact and light-weight lead acir1 battery as claimed in any of the preceding claims 1 to 5, wherein the length of the spines of the positive plates thereof is equal to, or less than about 90 mm. 7. The compact and light-weight lead acid battery as claimed in the preceding claim 6, wherein the height of the plastic caps of the positive plates thereof is equal to or greater than about 5 mm. 8. The compact and light-weight lead acid battery as claimed in preceding claim 8 wherein said batteiy box is of a transparent polycarbonate plastic material. 9. A compact and light-weight lead acid battery for applications such as miners lamps substantially as hereindeseribed with reference to and as illustrated in the accompanying drawirgs. 10. A miners lamp incorporating a compact and light-weight lead acid batter,' as claimed in any of the preceding claims 1 to 9.

Full Text

This invention relates to lead acid batteries and more particularly to compact and light-weight load-acid batteries for such applications as miners cap lamps.
Miners cap lamps are also referred to as miners lamps, miners safety lamps and by other terms. In this specification, the term miners lamo is used and is intended to cover the equivalent terms mentioned hereinabove and also said other terms used in the art.
Miners cap lamps generally comprise lead-acid batteries that form the subject of this invention. In this specification, therefore, the terra batter,' (ies) refers to lead acid batteries unless otherwise required by the context.
The battery of the invention is particularly relevant to miners lamps the batteries whereof are required to be compact and lightweight. In this specification, thcrelorc, Ihe application of batteries of the invention to miners lamp alone is considered. This is in the interests of conciseness and without affecting the scope of the invention. In this connection, it is stressed that there are other applications in which the compact, lightweight batteries of the invention could be used/adapted to.
Lead acid batteries may be made/traded with or without the electrolyte thereof. If with the electrolyte, the electrolyte may be contained in the battery itself or in a container separate of the battery. The term 'lrad acid battery' in the description and claims of this specification is intended to cover within the scope thereof the abovementioned and other possibilities
An electrical cell such as a lead acid cell provides electrical energy and comprisss a pair of conducting plates immersed in an electrolyte. A battery comprises a plurality of such cells

interconnected, or interconnectible, in series, or in parallel or in a series-parallel arrangement. A cell comprises also a container that houses the cell plates and holds the electrolyte thereof.
Two containers are involved in a battery, the cell container mentioned hereinabove and the battery container. As mentioned, the former houses the parts and contents of a cell while the latter houses the cells comprising the battery. In this specification, the former is referred to as the 'cell case' and the latter as the 'battery box' or 'cell box', both latter terms being interchangeably used in the specification.
Battery boxes (cell boxes) comprise compartments for housing the cells thereof. In one construction, cells complete with their cell cases are housed in said compartments. In another construction, said compartments are adapted to function as said cell cases, that is, they themselves form said cell containers wherein said cell plates and electrolyte are housed. It will be noted that in this construction said cell cases (cell containers) become redundant which results in considerable reduction in the overall weight and volume of a battery. Said elimination (of cell cases) has the effect of improving the energy density of the battery, said energy density being the Ampere-hours (Ah) capacity per unit weight or volume thereof.
Modem miners lamp batteries (miners batteries) are generally of said another construction wherein the cell boxes thereof are made of plastics. There are two reasons for the adoption of plastics therefor, one being that plastics offer considerable weight/volume savings in comparison to hard rubber cell boxes. The other is that transparent plastics cell boxes permit easy visual inspection of the contents of a cell. In the specification further hereinbelow, therefore, as in the art, said compartments are also referred to as cell cases.

Miners batteries are generally of 4V rating and comprise two lead acid cells each of 2V nominal capacity connected in series. This arrangement is also required by the standards adopted for miners batteries in various parts of the world, for example, IS:2512:1978 and BS:4945:1989. Thus a miners battery typically comprises a plastics cell box having two compartments therein each accommodating a lead acid cell, said two cells not comprising said cell cases, that is, said compartments themselves functioning as said cell cases as discussed hereinabove. The further specification hereinbelow is in reference to this construction only. This has been done in the interests of conciseness and without limitation to the scope of the invention.
In principle, a cell comprises a pair of plates, one positive and one negative. However, in modern
miners batteries, an additional negative plate is provided which is disposed such that the two negatives are located one on each side of the positive. This arrangement offers better utilisation of cell space in that both surfaces of the positive plate are then equally active in the cell process. This leads to a reduction in overall cell weight/volume and an increase in the energy density of the battery. It will be observed that in this construction, there are two pairs of positive-negative surfaces and consequently two separate current paths in the cell. The cell, in effect, constitutes two cells in parallel, that is, rather like a battery. However, said three plate construction is uniformly referred to in the field as a cell and this is the terminology adopted in this specification further hereinbelow. Thus, in this specification, a cell is understood to comprise three or more said plates arranged in an array wherein positive plates alternate with negative ones and the outermost plates of the array are negative, said array being housed in a said cell case (compartment). This is the construction referred to in the further specification hereinbelow although the arrangement in which the outermost plates of the array are positive is also within the scope of the invention.

While reference has been made to arrays of three or'more said plates it must be emphasised that arrays of only three plates per cell are found in the miners batteries of prior art. No instance was observed of a miners battery construction wherein the cells thereof comprised more than three said plates each. Furthermore, there is apparently no indication of said array expansion beyond three plates having been considered in prior art. There is apparently no comment in prior art whether such an expansion would be desirable or not, and if so, whether feasible or not. This invention provides for a five-plate array and the consideration and development by this invention of said expansion to a five plate array is novel. Said five plate array is in the form of a 2+3 arrangement, that is, two positive and three negative plates. This is further elaborated hereinbelow.
A miners battery of prior art comprises a plastics cell box having two said compartments (cell cases) each of which holds a lead-acid cell. A said cell has an array of three said plates, with the positive and negative plates being arranged alternately in the array and the two outermost plates being negative. The positive plate is of the tubular type and comprises a plurality of antimonial lead spines attached to a header (strap). Said spines and header are enclosed in a fabric gauntlet and the active material of the plate is packed in the spaces between said spines and gauntlet. The function of said gauntlet is to hold said active material and ensure good electrical contact between the active material and the header and spines. The function of said spines and header is to provide strength and rigidity to the plate as a whple. Said fabric gauntlet is required to prevent short-circuiting between the plates tiirough the active material and still to be permeable to the cell electrolyte and the ions contained therein.
Said negative plates are of the flat type. A flat type plate comprises a grid(lattice) of cast, injection moulded or other construction and is generally of antimonial lead. The active material of the negative plates is applied to said grids in the form of a paste and the paste is pressed onto

said grids and into the interstices thereof. As in the case of the positive plates, the negative grid and the active material thereof are enclosed in a fabric bag (envelope). Said grid provides support for the active material and furthermore, strength and rigidity to the plate as a whole. The function of said envelope is to prevent shorting of the plates through said active material of the negative plates. Said envelope is required to be permeable to the cell electrolyte and ions contained therein with the exception of antimony ions. Said negative envelopes are therefore, of microporous construction so as to prevent migration of antimony ions from the positive to the negative plates. Actually, the active material of negative plates is spongy lead while said paste comprises lead oxide. During the process of plate formation said oxide gets converted to spongy lead. However, the material on the plates is uniformly referred to herein as the active material whether the reference is to the plates before said formation or after. This has been done in the interests of conciseness and for simplifying the specification.
The active material on the positive plate is lead peroxide and on the negative, spongy lead. Said active materials may further comprise one or more of several additives/components used in the art for improving the performance of the plates. The cell electrolyte comprises dilute sulphuric acid of the appropriate density range. Said gauntlets are generally of a polyester fabric and said envelopes of negative plates of polyethylene. Said polyethylene bags prevent shorting between plates, caused by oxide deposition at the cell bottom.
Located between each pair of plates is a polyester separator whose function is to prevent electrical shorting between said pairs and also to absorb the cell electrolyte and render it immobile. A set of separators of a cell are designed to absorb about 85% of the electrolyte leaving only about 15% as free liquid. Said absorption helps in making the battery substantially spill proof. It also reduces gassing as the oxygen generated if any, at the positive plate, during charge or overcharge instead of rising to the top of the cell diffuses through said separator to the

negative plate where it is reduced to water by reaction with the lead of the negative plate and the acid in the electrolyte. The battery is provided with a vent for evolved gases if any, the vent comprising a labyrinthine passage designed to prevent spillage of acid through the vent. The vent also performs the function of the topping-up opening by means of which the level of electrolyte in the cell can be topped up to the desired level. In the cells of miners batteries, said packs (assemblies) of plates and separators thereof are always under compression. That is, the total width of said packs is designed to be marginally greater than that of said compartments such that when the packs are placed in their compartments they are slightly compressed.
Said battery box is provided with a lid that is joined to the former by means of processes such as heat-sealing, ultrasonic sealing, adhesive sealing, solution sealing or others as appropriate. Both said battery box and lid are usually of a transparent plastic such as a polycarbonate.
Level markings are provided on said battery box to indicate the electrolyte levels in both fully charged and discharged conditions. Two terminal posts of high antimony lead alloy are provided one for the positive plates and one for the set of negative plates of a cell. They are joined to their respective plates by welding and protrude through said lid into the battery cover. Said posts form the cell/battery terminals at the top ends thereof. Said battery cover is generally of stainless steel and is fixed onto said lid. A said battery or cell may comprise more than one pair of said terminals. The battery is provided with a fuse located on said lid.
The positive plates are usually of a high antimony lead alloy containing about four percent or more of antimony. For low maintenance batteries, a low antimony lead alloy is used for the positive plates, said low antimony alloy containing less than 3% antimony. Said low antimony alloys for plates often contain added grain refining elements, for example, selenium, copper, sulphur and others. The abovementioned alloys are also used for the negative plates.

For negative plates of low maintenance batteries antimony-free calcium lead alloys are often used. However, use of said calcium-lead low maintenance alloys is generally confined to negative plates.
The material of construction used for said cell boxes (battery boxes) are hard rubber, polycarbonates, ABS, polypropylene, fire retardant plastics and others.
Described hereinabove is a most commonly used design of a miners battery in the art. It is stressed that numerous alternatives are available in the art substantially for all of the design aspects considered above and others, such as the material of the battery box and lid and the method of closure thereof; alloys used for said positive and negative plates; type and material of said gauntlets, envelopes and said separators; methods of joining the various components and others. In the interests of conciseness, said design alternatives (variants) are not elaborated in detail hereinbelow. However, it must be noted that the miners battery of the invention can incorporate and be adapted to, each said variant. Thus, each said variant is within the scope of the invention in so far as it is provided on, or adapted to the battery of the invention.
A miners battery is expected to provide cyclic service, that is, working on a 24-hour cycle out of which during about 8 to 9 hours it is expected to be in the discharge mode. For the remainder of the time it is expected to be in the charge and storage mode. Typically, a miners lamp bulb draws about 0.8A which adds upto about 6.4 Ah of energy over a nine hour period. Considering a depth of discharge of about 75%, a 9 Ah capacity would be quite adequate for a miners battery and this is the standard capacity of one set of miners lamp batteries found in the art.
Increasing the ampere-hour capacity of a miners battery would provide two options:

i. increase the duration of said discharge mode while leaving the lamp (bulb) current
unchanged; and . ii. increase in lamp current while leaving the duration of discharge unchanged.
It will be noted that in the context of the application to miners lamps generally there is no scope of exercising the first option of increasing the duration of said discharge mode. The benefit of an increase of ampere-hour capacity can therefore, be realised only in the exercise of the second option, that is, increasing the bulb current. The art has therefore, developed 12 Ah capacity batteries for miners lamps wherein bulbs of higher rating, namely, 1,0A are used.
Miners work-shifts are generally of about eight hours duration but where they are of twelve hours duration there is scope for utilising said first option of a longer discharge mode.
This invention provides for a 16Ah miners battery and this is novel. The 16 Ah novel battery of the invention comprises said novel 2+3 plate arrangement, .that is, two positives and three negatives per cell. Thus, the battery of the invention provides the option of still further increase in bulb current so that bulbs of higher lumen rating may be used. Prior art has not considered/contemplated increase in ampere-hour rating beyond said 12 Ah perhaps because of the apparently insurmountable nature of difficulties observed by these inventors in carrying out said array expansion within the confines of the standard dimensions of prior art batteries and that laid down by various standards such as IS;2512:I978. This invention has provided said increased energy capacity together with said larger array, that is, said 2+3 arrangement within a battery box of substantially the same dimensions as of the said 12 Ah battery of prior art and as provided for by the abovenamed Indian standard. This is a further novel feature of the invention. Thus, the 16 Ah battery of the invention can be used in a miners cap lamp assembly comprising say a bulb drawing 1.25 A. Such a bulb would draw about 11.25 Ah over a nine hour period which would be

around 75% of the battery capacity. Said cap lamp would then be 'operating in cycling service at a depth of discharge (DOD) of around 75% which is quite within the limit generally accepted in the art for lead acid batteries in cyclic service. .
The battery of the invention also provides the option of using it in a cap lamp drawing a lesser current for example, with 1A bulbs as used in the 12 Ah miners batteries of prior art. In such an application, the battery of the invention would be operating at a still lower DOD value that would have the effect of enhancing the cycle life thereof. There would also be added advantages of reduced gas evolution and electrolyte loss (water loss) and reduced rate of irreversible sulphation of the plates.
The object of the invention was to develop a compact, lightweight battery having a higher energy capacity of 16 AH as opposed to the 12 Ah capacity of prior art batteries. A further object of the invention was to provide this additional capacity by addition of a pair of plates, one positive and one negative to the 12 Ah miners battery of prior art. That was to change said array configuration of (1+2 one positive and 2 negatives) of said prior art battery to a (2+3) configuration comprising two positives and three negative plates. A still further object of the invention was to obtain said increased capacity and said (2+3) arrangement within the battery box of same width as provided for in the batteries of prior art. A still further object of the invention was to develop extra-thin plates such as to allow said 2+3 arrangement within the battery box of substantially the same width as in the batteries of prior art. A still further object of the invention was to minimise the thickness of the separators with a view to accommodate said 2+3 arrangement as also to increase the proportion of free electrolyte in the cells. A yet another object of the invention was to minimise the maintenance requirements of the battery.

It will be observed that the increase in capacity from prior art to the battery of" the invention is about 33-1/3%. If this increase of capacity were to be provided by increasing the quantity of the active material on the plates both the packing density of the material on the plates and the current density of the plates would be correspondingly higher. The consequences of an increase in current density would be an increased tendency towards gassing. Further, the added active material would add to the internal resistance of the cell and this would enhance the voltage drop across the cell both during charging and discharging. This again will result in increased tendency towards gassing. Increased gassing requires increased maintenance attention to the battery in the form of more frequent toppings-up of the cells.
Increasing said packing density has an adverse effect on the porosity of the active material mass on the plates, particularly in case of tubular positive plates. One effect of decrease of said porosity is a decrease in the discharge current. It also leads to a poorer DOD.
This invention has achieved the object of minimising maintenance while avoiding the drawbacks mentioned hereinabove, by providing said increased capacity in the form of added plate surface. Thus, this invention provides for a (2+3) plate array configuration in place of the 1+2 array of prior art batteries. Change from a 1+2 arrangement to a 2+3 arrangement with plate dimensions remaining unchanged would substantially double the active plate area. As only about one-third increase of capacity is desired this invention provides the option of decreasing the plate dimensions somewhat. Accordingly, in this invention the plate height and breadth have been reduced from that in the 12 Ah prior art battery that, as explained hereinbelow, resulted in improvement in battery performance. The approximate dimensions of said 12 Ah prior art battery and the 16 Ah battery of the invention are displayed in Table 1.

Table -1

12 Ah Prior art battery 16 Ah battery of the
invention
Plate height in mm. 118 100.8
Plate breadth in mm. 66.7 57
The quantity of electrolyte provided in the 16 Ah battery of the invention can be somewhat greater, equal to or less than that in the prior art 12 Ah battery within the scope of the invention. In the embodiment described further hereinbelow, the quantity of electrolyte in the battery of the invention is somewhat less than that in the prior art battery such as to maintain substantially the same level of electrolyte in both. It may be noted that the dimensions of the battery box of the invention are substantially same as that of the 12Ah prior art battery. The battery of the invention therefore meets the requirement of the non-spillability test under IS 2512:1978.
This invention provides for extra-thin positive and negative plates and this is novel. The thickness of a positive plate in a 12 Ah battery of prior art is about 10.5 mm and of a negative plate about 3.60 mm. These thicknesses have been considered irreducible in prior art. This invention provides reduced plate thicknesses while at the same time adequate strength and rigidity for the plates. The novel thicknesses in the batteries of the invention are: for positive plates about 9.5mm and below and for negative plates about 3.4 mm and below. The positive plate thickness mentioned hereinabove includes the gauntlets thereof while for the negative plates the thickness figures exclude the envelopes thereof. Said extra-thin plates are novel and result in slimmer plate

packs. This makes it possible to accommodate a 2+3 plate configuration in the same generally 42 mm wide battery box as that used by the prior art 12 Ah battery. It may be mentioned that 65 mm is the maximum value of the. width laid down by IS:2512:1978 for miners cap lamp batteries. Thus, the width of the battery box in the battery of the invention is considerably less than that laid down under IS 2512:1978. The cell internal resistance is also reduced by the use of slimmer plate packs that incorporate said extra-thin plates of the invention.
The separators in the batteries of the invention are of the same material as that in the 12 Ah prior art battery but are of reduced thickness. This is novel. This has been done to bring down the width of said 2+3 plate pack sufficiently to be able to house it in the battery box of prior art. Said separator thicknesses are about 1.35 mm and 8.5 mm respectively for the battery of the invention and the prior art battery. This reduction of separator thickness also brings down the internal resistance of the cell. The separators comprise polyester pads.
Reduction in separator thickness could be expected to lower the amount and availability of the acid electrolyte in contact with the plates. This effect is countered in the battery of the invention by the increased proportion of tree electrolyte available in the battery of the invention in contrast to batteries of prior art.
Any adverse effects of the reduction in thickness of the plates from that in prior art have been
countered by the following factors as a result of which the performance of the battery of the
invention is equal to and in some respects superior to the prior art batteries.
i. increased said porosity obtained because of reduction in quantity of active material per
unit plate area;
ii. the availability of a larger proportion of free electrolyte following the reduction in
separator thickness;

In summary the novel and advantageous features of the battery of the invention are:
i. a higher electrical capacity and a higher energy efficiency of watt-hr/kg and watt-
hr/cu.cm; ,
ii. a 2+3 array;
Ui. reduced plate thicknesses leading to reduced internal resistance of ceil,
iv. reduced separator thickness leadinp to reduced internal resistance of cell;
v. less tendency towards gassing because of reduced internal resistance of cell, reduced
packing density of active material on plates and reduced current density in the cdl; vi. greater proportion of free electrolyte than that in prior art battery; vii. use of a low maintenance alloy (low antimony lead alloy) for the positive plates; viii. increased height of the bottom caps for the positive plates which reduces the risk of
shorting still further over that in prior art batteries; and
ix. reduced height of said spines .which improves the castability thereof, in particular casting
under pressure.
According to the invention, therefore, there is provided a compact and light-weight lead-acid battery for such applications as minsrs lamps, comprising a plurality of lead acid cslls, each said cell comprising an array of alternating positive and negative plates with separators interposed therebetween, characterised in that at least one said array therein comprises five said plates.
The battery of the invention comprises two or more lead acid cells wherein one mcc or all of said cells may comprise the novel 2+3 array, that is, pack of two positive and three negative plates together with their separators. In one embodiment which is particularly applicable to miners lamps, the battery of the invention comprises two said cells each of which comprises said novel 2+3 array of plates. The embodiment described further hereinbelow is of a miners battery and is in general accordance with IS 2512:1978 for miners batteries.

This invention provides for extra-thin plates, that is, positive plates of thickness equal to. or less than about 9.5 mm and negative plates of thickness equal to or less than about 3.4 mm. One, more or all of the plates of the battery of the invention may comprise said extra-thin plates. Said thickness values include the gauntlets in the case of positive plates whereas in the case of negative plates the thickness refers to the bare plate exclusive of the envelope thereof. In the embodiment described, all the five plates of each of the two cells are extra-thin. The thickness of said plates in the embodiment described herein are about 9.5 mm and 3.25 mm respectively for the positive and negative plates.
The invention also provides for slim separators of thickness 1.35 and below. The five extra-thin plates in a cell together with four of said slim separators constitutes a pack which is placed in a said compartment of a cell box. The width of said pack is such that when in position in said compartment it is under slight compression. The width of the pack in the compressed state comes to about 36 mm which together with the thickness of the sides of said compartment adds upto about 42 mm the outside width of the battery box. The Indian Standard IS:2512:1978 lays down a maximum width of 65 mm for the battery box of a miners battery. This figure includes the projections of the belt loops located on the surface of the battery box body. The embodiment described conforms to said standard in respect of the dimensional requirements and other requirements including the non-spillability test. The thickness of separators in the embodiment described herein is about 1.3 mm.
The battery box including the lid thereof are of a transparent polycarbonate in the embodiment described and the sealing is by use of appropriate solvents. Other materials of construction for the battery box and lid such as polypropylene and the use of other sealing methods are within the scope of the invention.

The positive and negative plates are both ofantimonial lead of about 2.5% Sb in the embodiment described. It is quite feasible to use other alloys such as are used in the batteries of prior art, such as, for example, calcium-lead alloys and these are within the scope of the invention. It is also feasible to use pure lead for plate construction but the use of both pure lead and said other alloys is associated with drawbacks. The option of using different alloys for the positive and negative plates is also within the scope ofthe invention.
The positive plate comprises a header wherefrom extend said spines thereof. Each header has one or more connection lugs that are joined to a terminal post by welding or other means. Said terminal post extends through said battery box lid and into the space between said lid and the battery cover top. The top ofthe terminal post constitutes the battery terminal and is located in said space.
The negative plate is in the form of a grid complete with the interstices thereof. Said grid plates are made by casting, injection-moulding, expansion or other processes. Various patterns and sizes of grids and interstices are used in the art and are within the scope of the invention. The active material is pressed onto the negative plate and into said interstices. The construction of said terminal posts, lugs and other components is similar to that in the case of the positive plates. A miners battery comprises two each of said positive and negative .battery terminals for each cell and the terminals of the two cells are connected in series to provide a nominal voltage of 4V for the battery. This is the construction provided in the embodiment described further hereinbelow.
The gauntlets ofthe positive plates are of a polyester fabric in the embodiment but may be of one of several suitable fabrics provided in the art. The gauntlets are made from woven fabrics by stitching or heat-sealing. They are placed around said spines and the space between the gauntlets

and spines is filled with the required amount of the active material of the positive plates. The lower end of the gauntlet, that is, of the positive plate is capped by a generally oval cup-like member. The function of said cap is to hold the active material and to prevent both shedding of the active material and shorting between plates. The gauntlets ensure adequate contact between the active material and the spines and prevent said shorting. The gauntlets are required to be permeable to the electrolyte and the ion components thereof.
The envelopes of the negative plates are of woven polyethylene in the embodiment but several other materials are available for the purpose in the art and are within the scope of the invention. Said envelope is in the form of a bag made from polyethylene sheet /fabric and are formed by heat-sealing. Said bags are slipped over the negative plates, one for each plate. The bags prevent shorting of the plates and oxide deposition at the bottom of cells and are permeable to the electrolyte and the ions contained therein with the exception of antimony ions.
Said separators consist of polyester pads in the embodiment described. They absorb the electrolyte in the pores thereof and render it substantially immobile. The absorption of the bulk of the electrolyte by said separators makes the battery substantially non-spi liable. The quantity of the electrolyte in a cell is adjusted so that a certain amount of the pores in said separators remain unfilled, that is, free of electrolyte. The unfilled pores provide channels for diffusion of gases between plates. In particular, oxygen evolved if any, at the positive plates during charging or overcharging diffuses across to the negative plates where it is reduced to water by reaction with the spongy lead of the negative plates and the acid in the electrolyte. In this manner, water lost from the electrolyte by gassing is substantially returned back to the electrolyte making the battery substantially maintenance-free. Several other materials for said separators are provided in the art and are within the scope of the invention.

The invention provides for said plastic caps of a larger height of about 5 mm than those provided in prior art. This further reduces the risk of shorting occurring through the lower ends of the positive plates. This is novel.
Said spines in the battery of the invention are of a smaller length than provided in prior art. The decrease in said length has been partly possible because of the decrease in the height of the positive plates of the battery of the invention over that in prior art. In the prior art miners batteries, the length of said spines is of the order of 110 mm against a plate height of 118 mm. The decrease in the plate height of the battery of the invention over that in prior art provided scope for a proportionate reduction of said length. This invention has gone further in reducing said spine length down to about 90 mm and below. This has resulted in better castability of the header-lug-spines assembly that is, in reduction in rejects. This has been achieved while maintaining the performance of the battery of the invention to the level of the prior art batteries. Said spine length in the embodiment described hereinbelow is about 90 mm.
In order to provide a clearer understanding of the invention, an embodiment thereof will now be described without limitation to the scope of the invention and with reference to the accompanying drawings wherein:
Fig. 1 shows an isometric view of the battery of the invention;
Fig. 2 shows an exploded view of said pack of plates and separators of the battery of the
invention, and
Fig. 3 shows the maximum dimensions ofa miners battery as laid down in IS:2512:1978 with the
corresponding dimensions of the battery of the embodiment shown in brackets.

Reference numeral 1 in Fig. 1 denotes the battery box (cell box) having lid 2 which is attached thereto by solvent welding. Cell box 1 comprises two compartments 3,4 which house the two cells of the battery. Each cell comprises a pack (assembly's, of positive plates 6 and negative plates 7 and the separators 8 thereof. Each positive plate 6 comprises header 9, spines 10 and connection lug 11 all made of a low-antimony selenium lead alloy. Header 9 and spines 10 of a positive plate are enclosed by a gauntlet 12 made of a polyester fabric. Each positive plate is provided with a plastic cap 13 at the lower end thereof. Said caps 13 are applied after the gauntlets 12 are filled with the active material 14 of the positive plates. Gauntlets 12 together with caps 13 hold the active material 14 and ensure good electrical contact between spines 10 and the active material. They also prevent shedding at positive plates and shorting between plates.
Negative plates 7 comprise cast grids 15 of a low antimony selenium lead alloy. Grids 15 have interstices 16 that hold the active material 17 of the negative plates. Plate active material is applied to grids 15 and interstices 16 in the form of a paste which is pressed upon the grids and into said interstices. Negative plates undergo a process of formation during which said paste material is converted into spongy lead, the active material of the negative plates. Each negative plate 7 is enclosed in an envelope 18 which covers both sides thereof. Envelope 18 is of microporous polyethylene and is in the form of a bag that is made from polyethylene sheets by heat-sealing or solution-sealing. Gauntlets 12 and envelopes 18 hold the active material of the respective plates and prevent shorting between the plates. They allow free diffusion of the electrolyte 19 and ions between the plates.
Located between each positive-negative plate pair 6,7 is a separator 8 that comprises a porous polyester pad. Pads 8 absorb electrolyte 19 and allow diffusion of oxygen gas from positive to negative plates. Most of the oxygen liberated, if any, at the positive plates thus eets transoorted

to the negative plates where it is converted to water and returned to the electrolyte. Separators 8 allow diffusion of the electrolyte between the plates.
Said connecting lugs U of a cell are connected to the positive terminal post 21 which extends upwards through said lid 2. The top end of terminal post 21 forms the positive terminal 22 and is located in the space between said lid 2 and battery cover 30. The lugs 23 of the negative plates 7 are also connected together and to the negative terminal post 24. Terminal post 24 similarly extends above said lid 2 and has the negative terminal 25 at the top end thereof.
Vent openings 26 vent any gas that is released in the cell and that is collected in the space above the electrolyte. While most of the oxygen evolved at the positive plates diffuses to the negative plates through said separators and is recycled as mentioned hereinabove a small quantity thereof may collect above the electrolyte and is vented out of the cell. Said vent openings 26 include a non-spill device 27 which comprises a labyrinthine passage that allows gas to escape but holds back the electrolyte. The two vent openings 26 of the battery are solution-jointed to the battery box.
A pair of level indicating marks 28 are provided for each cell. Said marks indicate the desired electrolyte level in the cell both in the fully charged and discharged condition thereof. During maintenance water is added to the cell to make up for the water lost if any. Said topping-up is made to the appropriate mark. Addition of water to the cells is done through said vents 26 that also function as openings for topping-up.
Gaskets 29 are provided at terminal posts 21,22 to provide seal between said posts and lids 2. The battery is provided with top cover 30 that is of stainless steel. Cover 30 comprises insulating

pads of PVC located on the top inside surface thereof so as to prevent shorting between said posts. Battery fuse 31 is located on lid 2.
The material charged into the gauntlets 12 of positive plates 6 comprises a mixture of lead oxides which during the formation process of the plates gets converted to lead peroxide, the active material 14 of the positive plates. Similarly, the paste applied to the negative plate grids at the time of manufacture comprises lead oxide which during said formation process gets converted to spongy lead. Said spongy lead constitutes the active material 17 of the negative plates. Said active materials may contain one or more of several additives provided in the art for enhancing the performance of the battery.
During discharge, the active material of both the positive and negative plates gets converted to lead sulphate which gets regenerated back to the respective active materials during the charging operation.
Cover 30 is provided with looping/locking means 32 for the cable that would run from the battery of the invention to the cap lamp when the two are assembled. Means 32 ensure that said cable is not pulled off during use of the battery and the cap lamp. Belt loops 33 are provided on battery box 1 for attaching the battery to the waist-belts used by miners.
Various embodiments and variations other than described above which are within the art are within the scope and spirit of the invention.

We claim:
1. A compact and light-weight lead acid battery for such applications as miners '^nps comprising a plurality of lead acid cells, each said cell comprising an array of alternating positive and negative plates with separators interposed therebetween, characterised in that at least one said array therein comprises five said plates.
2. The compact and light-weight lead acid battery as claimed in the preceding claim 1 wherein the outermost plates of the arrays are negative.
5. The compact and light-weight lead acid battery as claimed in the preceding claim 2 having a capacity of about 16 Ampere-hours.
4. The compact and light-weight lead acid battery as claimed in the preceding claim 3, wherein the thickness of said positive plates is equal to, or lower than, about 9.50 mm and of said negative plates is equal to, or lower than, about 3.4 mm.
5. The compact and light-weight lead acid battery as claimed in preceding claim 4, wherein the thickness of said separators is equal to, or lower than, about 1,35 mm.
6. The compact and light-weight lead acir1 battery as claimed in any of the preceding claims 1 to 5, wherein the length of the spines of the positive plates thereof is equal to, or less than about 90 mm.
7. The compact and light-weight lead acid battery as claimed in the preceding claim 6, wherein the height of the plastic caps of the positive plates thereof is equal to or greater than about 5 mm.
8. The compact and light-weight lead acid battery as claimed in preceding claim 8 wherein said batteiy box is of a transparent polycarbonate plastic material.
9. A compact and light-weight lead acid battery for applications such as miners lamps substantially as hereindeseribed with reference to and as illustrated in the accompanying drawirgs.

10. A miners lamp incorporating a compact and light-weight lead acid batter,' as claimed in any of the preceding claims 1 to 9.

Documents:

0667-mas-2001 abstract duplicate.pdf

0667-mas-2001 abstract.pdf

0667-mas-2001 claims duplicate.pdf

0667-mas-2001 claims.pdf

0667-mas-2001 correspondence-others.pdf

0667-mas-2001 correspondence-po.pdf

0667-mas-2001 description (complete) duplicate.pdf

0667-mas-2001 description (complete).pdf

0667-mas-2001 drawings duplicate.pdf

0667-mas-2001 drawings.pdf

0667-mas-2001 form-1.pdf

0667-mas-2001 form-19.pdf

0667-mas-2001 form-26.pdf

0667-mas-2001 petition.pdf

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Patent Number

201056

Indian Patent Application Number

667/MAS/2001

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

Date of Filing

14-Aug-2001

Name of Patentee

EXIDE INDUSTRIES LTD

Applicant Address

OLDHAM DIVISON. 21/22, ALANDUR ROAD, GUINDY, CHENNAI - 600 032

Inventors:

#	Inventor's Name	Inventor's Address
1	MR. CHELLIAH SAMUEL, CONSULTANT	HEAD-TECHNICAL EXIDE INDUSTRIES LTD, OLDHAM DIVISON. 21/22, ALANDUR ROAD, GUINDY, CHENNAI - 600 032
2	MR. SURENDER JOSEPH	HEAD-TECHNICAL EXIDE INDUSTRIES LTD, OLDHAM DIVISON. 21/22, ALANDUR ROAD, GUINDY, CHENNAI - 600 032

PCT International Classification Number

H01M10/42

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA